The purpose of the present study was to investigate the L2 use rate in EFL classrooms through introducing three task conditions in learning lexical items. Data were collected from a group of freshman university students (male and female) studying in Islamic Azad university of Sabzevar, Iran (N = 73). Based on their performance on a Michigan TOEFL reading test battery, they were first randomly divided into three groups, each completing one of the three vocabulary learning tasks that varied in the amount of L1/L2 use they induced during a two month period. The tasks were "Reading plus further L2 reading", "Reading plus L1 translation only" and "dictionary work". The statistical analysis of the students' performance on vocabulary post-tests was performed through One-Way ANOVA followed with the post hoc Regression Scheffe test to analyze which task has created a meaningful mean variability at 0/05 for both between and within groups. The results showed the outperformance of the group receiving "reading plus further L2 reading" tasks and not the tasks involving more L1 use. (p:<0.05) Possible implications of the study are presented in the light of Task Load Involvement Hypothesis by (Laufer & Hulstijn, 2001).